Unwind stand web tension control system



Sept. 15, 1970 H. E. ROSCOE v UNWIND STAND WEB TENSION CONTROL SYSTEM Filed Sept. 17. 1968 s Sheets-Sheat 1 ,4c+uA1'Eo v TO cur ou-r BRAKE 76 Sept. 15, 1970 H. E. ROSCOE 3,528,620

UNWIND STAND WEB TENSION CONTROL SYSTEM Filed Sept. 17, 1968 s Sheets-Sheet- 2 INVENTOR HOWARD E. ROSCOE BYJMWV ATTORNEYS Sept. 15, 1970 H. E. ROSCOE UNWIND STAND WEB TENS Filed Sept. 17. 1968 ION CONTROL SYSTEM 3 SheetsvSheet 5 INVENTOR. HOWARD E. ROSCOE mar/ga ATTORNEYS United States Patent 3,528,620 UNWIND STAND WEB TENSION CONTROL SYSTEM Howard E. Roscoe, Green Bay, Wis., assignor to FMC Corporation, San Jose, Calif., a corporation of Delaware Filed Sept. 17, 1968, Ser. No. 760,329 Int. Cl. B6511 19/16 US. Cl. 242-584 7 Claims ABSTRACT OF THE DISCLOSURE Dual brakes operating together vary the braking torque applied to an unwinding mill roll of web material that is fed to a printing press and means are provided for releasing one of the brakes as the web unwinds to extend the useful range of brake control. Stoppage of the printing process to change rolls is obviated by forming a continuous web with flying splices between the webs of full mill rolls and expiring mill rolls. To facilitate such splicing and reduce inertia stress in the web, a nest of splicing rolls are adjustably mounted for location in the optimum web splicing position.

BACKGROUND OF THE INVENTION Field of the invention Description of the prior art During operation of a flexographic printing press, a mill roll of web material is continuously unwound and fed through the press where it is acted upon at various stations and then rewound upon a storage roll. Constant tension should be maintained in the unwinding web because variations in tension can result in an irregular printing repeat length when measured in a relaxed condition. Thus, when the web is fed to a converting machine, such as a wrapper or bag machine, variations in length will cause the printing to be out of place. This is an acute problem when the material printed upon is of light gauge and low stiflness such as polyethylene.

The customary web tension control for unwinding mill rolls feeding flexographic presses is to use a braking system either directly connected or geared into the unwinding mill roll. As the Web is pulled through the press, a tensile force is applied to the web which in turn is trained about a tension sensing roll of either the counterweighted dancer style or of the load cell type. This tension sensing roll continuously feeds a signal to the braking system to adjust the retardation torque setting of the brake. Should the web tension be below the predetermined amount, additional brake torque is applied, while excessive web tension causes the brake torque to be decreased.

It is desirable to use a press for printing on webs having a wide variety of width, length, gauge and stiffness characteristics. Furthermore, it is desirable to use large diameter mill rolls to reduce the number of splices in a printing run. To fit this degree of variation, brakes are sized large enough to fit the heavy gauge, wide width and large diameter mill rolls and change gears are provided to decrease the torque output of the brakes for light gauge, narrow width and small diameter mill rolls. In addition, brakes have upper and lower torque limits that 3,528,620 Patented Sept. 15 1970 control design so that it is difiicult to obtain wide flexibility with a single directly connected brake. A brake designed for maximum loads may release and grab when the light gauge web material approaches the core diameter because of the lower torque limit of the brake.

When printing on a continuous web of material that comes in mill rolls, it is desirable to use a turret type of unwind stand so that flying splices can be made without stopping the printing process. Such a splice is made by applying adhesive tape or glue to the web tail of a full mill roll and dropping the tail in a nest of rotating splicing rolls through which the expiring web flows. A pull start is given to the full mill roll to overcome inertia and any remainder of inertia load must be absorbed by the web material. This presents problems when the web material is weak or brittle and the mill roll is heavy.

The above splicing method is simple, economical, and works well with common web materials such as polyethylene, providing the unwind stand is designed to include a good arrangement for splicing. Such an arrangement would meet the following conditions:

1) The mill roll must be capable of starting with either a clockwise or counterclockwise rotation as the web material may be treated on one side only to accept printing.

(2) The mill roll and its tail should be accessible with an unimpeded arms reach.

(3) The tail when dropped should be trapped between the rolls with the expiring web.

(4) The adhesive material on the new web should be pressed to the expiring web by the nip pressure between two rolls, preferably more than one.

(5) The expiring web should be the uppermost Web as-it passes overhead to the fiexographic press. With this arrangement the new web acts as a carrier for the web and prevents the old webs tail from dropping into the machine at low speed.

All of the above conditions cannot be met by one fixed geometrical arrangement and press manufacturers currently mount two or three splicing rolls in a compromise position which violates one or more of the above conditions.

SUMMARY OF THE INVENTION A braking system has two brakes geared to an unwinding mill roll that operate together to apply braking torque and means are provided for releasing one of the brakes as the mill roll unwinds to enable the remaining brake to operate above its lower torque limit. Such a result is achieved because a tension sensing roll adjusts a power supply to the remaining brake for single brake action. This enables the braking system to maintain constant web tension for a wide range of web gauges, widths and mill roll diameters.

A nest of splicing rolls are adjustably mounted on the unwind stand for location in the Optimum position for splicing webs unwinding in a clockwise direction and moveable to the optimum position for splicing webs unwinding in a counterclockwise direction. This enables all of the conditions for a good splicing arrangement to be met and thus, an operator can make flying splices without stopping the printing process and with a minimum amount of inertia absorbed by the web.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of a flexographic printing press.

FIG. 2 is a front elevation of an unwind stand embodying the present invention.

FIG. 3 is a section taken on the line 33 of FIG. 2 illustrating a position for splicing rolls unwinding in a counterclockwise direction.

3 FIG. 4 is a section similar to FIG. 3 but illustrating a position for splicing rolls unwinding in a clockwise direction.

FIG. 5 is a schematic illustration of an unwind stand together with a tension sensing roll.

'FIG. 6 is a control diagram for a dual braking system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Looking now at FIG. 1, a flexographic printing press '10 is shown having an unwind stand 11 at which a web 12 is unwound from a mill roll 13. The mill roll is supported at one end of a turret mechanism 14 that is capable of supporting a standby mill roll at the opposite end and to facilitate splicing and loading of mill rolls; the turret mechanism is rotatabe with shaft 15. This shaft has a worm wheel 16 mounted thereon driven by a worm 17 that is interconnected by a drive '18 to a motor Web 12 that is unwound from mill roll (13 passes through a nest of splicing rolls 21 and continues over a tension sensing roll 22 effective to control in-feed tension on the web. The splicing rolls are interconnected with the tension sensing roll by a brake assembly, not shown, that holds the tension sensing roll in a fixed position when splicing. From the in-feed tension section, the web passes upwardly and is suspended below a main drying oven 23 to a draw roll 24, from whence it passes around the outer periphery of a large diameter cylinder 25. A multiplicity of printing cylinders 26 and dryer hoods 27 are located about the periphery of the large diameter cylinder to apply multicolored printing ink to the web and high velocity drying air to the applied ink.

From the cylinder 25, the web is guided through a chamber inthe main drying oven 23 where it is subjected t0 heated air supplied by the main dryer burner and supply fan 29. As the printed and dried web leaves the oven, it passes by a web viewer 30 where it is inspected before passing on to dual cooling rolls 31. The web then passes an outfeed pinch roll 32 and continues around a tension sensing roll 33 that controls a taper rewind motor, not shown, for regulating the rewinding of the web on a storage roll 34. Powder can be applied to the web by an applicator '35 to prevent offset printing as the web is rewound and if it is desired to trim the web Width, a slitting station 36 including a razor, score or shear is provided.

Some printing presses extend over 30 feet from end to end and over 100 feet of web passes through the press between the unwinding mill roll -13 and the rewinding storage roll 34. Tension in this unwound web is controlled by the tension sensing roll 22 that regulates the in-feed web, while tension in the out-feet web is regulated by tension sensing roll 33. This invention relates to the in-feed web tension control at the unwind stand 11.

With reference to FIG. 2, unwind stand ill includes a frame having a left pedestal 38 and a right pedestal 39 that stand upon and are bolted to a support floor 40. A bracket 41 is pivotably mounted on a bolt 42 that is threaded into pedestal 38 and a similar bracket 43 is pivotably mounted on a bolt 44 that is threaded into pedestal 39. A lock 45 of the spring loaded plunger type extends through bracket 41 and fits in either a first hole 46 or a second hole 47 formed in the pedestal 38 to hold the bracket in the positions shown in FIG. 3 and FIG. 4, respectively. A similar lock 45 is provided to secure bracket 43 in position on pedestal 39.

A first shaft 48 extends between brackets 41 and 43 and has a splicing roll 49 rotatably mounted thereon, while a second shaft 50 extends between the brackets with a splicing roll 51 rotatably mounted thereon. An arm 52 (FIG. 3) is pivotably connected at one end to bracket 41, while the opposite end of the arm is connected to a pneumatic cylinder 53 suspended from the bracket. Similarly, an arm 54 is pivotably connected to bracket 43 and to a pneumatic cylinder 55. Shaft 56 extends between arms 52 and 54 and a splicing roll 57 is rotatably mounted thereon. A lower stop 58 is fixed to bracket 41 to limit the downward movement of arm 52 while an upper stop 59 is fixed to the bracket above the arm to limit the upward movement thereof. Bracket 43 has similar stops that carry out the same limiting function. Splicing roll 57 is normally positioned in an upper idling position out of contact with the other splicing rolls but upon actuation of the pneumatic cylinders, splicing roll 57 moves into contact with splicing rolls 49 and 51.

At the upper ends of the pedestals 38 and 39 are suitable bearings that journal the turret shaft 15 upon which a left turret arm 61 and a right turret arm 62 are mounted. A first core shaft 63 is journaled within the upper ends of the turret arms and extends therebetween to support a standby mill roll 64, while a second core shaft 65 is journaled within the lower ends of the turret arms and extends therebetween to support an expiring mill roll 66. A web 67 hangs down from the standby mill roll and is provided with an adhesive strip 68 at the lowermost end, while a web 69 depends from the expiring mill roll and is trained about splicing roll 57.

Mill rolls 64 and 66 are free to rotate with a pull on webs 67 and 69, respectively, and such rotation of the mill rolls causes the respective core shafts 63 and 65 to rotate. A stu b shaft 71 is coupled into the core shaft 63 for rotation therewith and extends outward from turret arm 62 to where a first change gear 72 is fixed to the end of the stub shaft. A shaft 73 is journaled in turret arm 62 and a second change gear 74 is mounted thereon to mesh with the first change gear. These change gears have a suitable gear ratio to increase braking torque for heavy mill rolls and when reversed, will decrease braking torque for light mill rolls. A pneumatic brake 75 is fixed to the turret arm 62 and an internal rotating part of the brake is fixed to an end of shaft 73 that extends therein. A second pneumatic brake 76 is fixed to the turret arm 62 and a shaft 77 is coupled with the internal part of the brake, journaled within the turret arm, and has a gear 78 fixed thereon. A gear 79 is fixed to shaft 73 and meshes with gear 78 having the same number of teeth so that shaft 77 is driven at the same speed as shaft 73. Air is supplied to brake 75 by a supply line 80 that extends from a rotary coupling 81 and a supply line 82 connects this rotary coupling with brake 76. A three-way air valve 82a and a flow control valve 8212 are provided in supply line 82. A central passageway 83 extending longitudinally of shaft 15 connects the rotary coupling with an air pressure valve later described, and a slip ring 84 is providedaround the shaft 15 to supply electrical current to operate the three-way air valve 82a.

An arrangement of shafts, gears and pneumatic brakes are coupled to core shaft 65, but since they are similar to those connected to core shaft 63 and described above, no further detailed description will be given.

FIGS. 5 and 6 illustrate how the tension sensing roll 22 regulates the pneumatic brakes 75 and 76. The tension sensing roll shown is a dancer type roll supported by an endless chain 86 that is trained about sprocket wheels 87 and 88. A counterweight 89 is suitably coupled to the endless chain opposite the tension sensing roll so as to balance the roll for the predetermined web tension. Sprocket wheel 87 is mounted on a shaft 90 and a gear 91 is mounted on the same shaft. A gear 92 is in mesh with gear 91 and turns a shaft 93 upon which a cam 94 is mounted. An air regulator 95 is contacted by the cam and, as shown in FIG. 6, this air regulator controls the air flow between an air source 96 and the central air passageway 83. An air pressure valve 97 positioned between the air regulator and the central air passageway and operates a relay switch 98 in an electrical circuit that controls the three-way valve 82a.

Operation of the tension control system begins with the counterweight 89 balancing the tension sensing roll 22 for the desired web tension. Should tension in web 12 be increased, the tension sensing roll 22 will move downward, rotating the endless chain 86. This rotation is transmitted through gears 91 and 92 to the cam 94 which actuates the air regulator 95 to decrease the air supply to the pneumatic brakes 75 and 76. A decrease in web tension would cause a reverse operation. Normally, as a web unwinds from a mill roll, the mill roll must continually accelerate and the air pressure is thus reduced from a maximum at the start of a full mill roll to a minimum at the core. Both of the pneumatic brakes are energized at the start of a full mill roll. As the air pressure drops to half of the maximum amount, air pressure valve 97 closes the relay switch 98 and three-way valve 82a is energized to move to an exhaust position. The air pressure to brake 76 is thus eliminated but flow control valve 82b prevents a sudden reverse air flow so that the tension sensing roll 22 can gradually rise. Thus, the air pressure from air regulator 95 is reset for single brake actuation, increasing the pressure at brake 75 to approximately the maximum. Then as the mill roll unwinds to the core, brake 75 is effective throughout the entire range from an upper torque limit to a lower torque limits.

The above system will permit using small air controlled brakes to provide constant tension braking for a wide range of web tension and mill roll diameters. The automatic dropping off of one brake partway through the unwind process is necessary when the ratio of the outside diameter of a mill roll divided by the core diameter exceeds 10. This is based upon limiting the torque of the brake to its heat dissipation rating, wear life, and the use of air regulators having an operating range of from three pounds per square inch to thirty pounds per square inch.

As the mill roll unwinds approaching the core, such as roll 66 in FIG. 3, a standby roll 64 is positioned so as to make a flying splice between web 67 and web 69. An adhesive strip 68 is prepared on web, 67 and an operator gives a pull start to the mill roll 64 so that the adhesive strips drops vertically between splicing rolls 57 and 49 and contacts the upper surface of web 69. Pneumatic cylinders 53 and 55 are actuated forcing splicing roll 57 against splicing rolls 49 and 51 so that nip pressure is applied to the adhesive strip in two places. Then as the splice passes overhead towards the cylinder 25, as shown in FIG. 1, the expiring web 69 is in an uppermost position and new web 67 acts as a carrier preventing the tail of web 69 from dropping around the printing cylinders 26 or dryer hoods 27.

Should it be desired to print on the opposite web side so that the mill rolls must be undound in a clockwise direction, as shown in FIG. 4, before starting the printing run, lock 45 is disengaged and brackets 41 and 43 are pivoted from the position shown in FIG. 3 to the position shown in FIG. 4. The lock 45 engages within hole 47 (FIG. 3) to hold bracket 41 in place, as shown in FIG. 4. A standby mill roll 64a and an expiring mill roll 66a are arranged as shown in FIG. 4 has an adhesive strip 68a applied to the end of the web 67a and when it is desired to make a splice to the tail end of the web 69a of the expiring roll 66a, the same procedure as given above in reference to FIG. 3 will be followed. It will be noted that both the splicing positions shown in FIGS. 3 and 4 meet all of the conditions for a good splicing arrangement as previously set forth.

It will be understood that certain modifications can be made in the structure described above without departing from the scope of the invention. For instance, it may be desirable to use electric disc brakes or electric particle brakes instead of the pneumatic brakes 7-6 and 66. In such case an electrical circuit would be provided wherein a potentiometer would be substituted for the cam 12 and air regulator 95 so as to vary voltage with rotation of shaft 93. A voltage relay would be substituted for airpressure valve 97 and it would operate a switch taking the place of three-way valve 82a. Flow control valve 82b would be replaced by a motor operated potentiometer to allow the tension sensing roll 22 to slowly rise when brake 76 is released. Another possible modifications would be to use a load cell type of tension sensing roll instead of the dancer roll 22 and this would also take the place of the potentiometer which was substituted for the cam and air regulator.

Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as set forth in the appended claims.

Having completed a detailed description of the invention so that those skilled in the art could practice the same, I claim:

1. An unwind stand comprising a frame; a pair of turret arms mounted on said frame for supporting a first mill roll in a position for unwinding a web therefrom in either a clockwise or counterclockwise direction and for. supporting a second mill roll in a standby position for unwinding a web therefrom in the same direction as the first mill roll; and a plurality of splicing rolls mounted on said frame beneath the pair of turret arms for splicing the web tail of the second mill roll to the expiring web of the first mill roll; said plurality of splicing rolls being mounted for movement between an optimum position for splicing webs unwinding in a clockwise direction to an optimum position for splicing webs unwinding in a counterclockwise direction.

2. An unwind stand as described in claim 1, including a pair of brackets pivotally mounted on said frame which support the splicing rolls that extend between the brackets, and means for locking the pair of brackets and splicing rolls in an optimum position for splicing webs unwinding in a clockwise direction and in an optimum positionfor splicing webs unwinding in a counterclockwise direction.

3. An unwind stand as described in claim 1, wherein the splicing rolls include a pair of outer rolls and an intermediate roll positioned between the outer rolls, and the splicing rolls are positioned so that the web tail of the second mill roll can drop between the intermediate roll and one of the outer rolls, travel about the intermediate roll and pass upward between the intermediate roll and the other outer roll along with the expiring web of the first mill roll.

4. A web tension control system at an unwind stand comprising a frame; a pair of arms mounted on said frame; a core shaft journalled within said arms supporting a mill roll in a web unwinding position; a tension sensing roll in engagement with the unwinding web of the mill roll; a first brake interconnected with the core shaft to apply braking torque thereto; a second brake interconnected with the core shaft to apply braking torque thereto; said' first and second brakes being connected to a source of power regulated by the tension sensing roll; and means for releasing one of said brakes while the web is unwinding to enable the other brake to apply braking torque to the core shaft in response to the tension sensing roll operating for single brake control.

5. A web tension control system as described in claim 4, including a first gear which rotates with the core shaft; a second gear in mesh with the first gear, and a shaft driven by the second gear and regulated by one of said brakes; said first and second gears having a different number of teeth to provide for a change of speed between the core shaft and the shaft driven by the secondgear and being interchangeable to enable different settings of brake torque output relative to the core shaft.

6. A web tension control system as described in claim 4, wherein said means for releasing one of said brakes releases the brake automatically as the web is unwinding.

7. An unwind stand as described in claim 1, including a core shaft journalled within said turret arms supporting 8 the first mill roll; a tension sensing roll in engagement References Cited with the unwinding web of the first mill roll; a first brake UNITED STATES PATENTS mterconnected with the core shaft to apply braking torque thereto; a second brake interconnected with the 2,472548 6/1949 Schneu 242-7543 core shaft to apply braking torque thereto; said first and 2,869,684 1/1959 Tif'rbuck 242 75-43 X second brakes being connected to a sources of power 5 3,072354 1/1963 61165 et a1 24258-4 regulated by the tension sensing roll; and means for releasing one of said brakes while the web is unwinding to NATHAN MINTZ Primary Exammer enable the other brake to apply braking torque to the c1 core shaft in response to the tension sensing roll operat- 10 242 75,43 ing for single brake control. 

